A problem associated with non-digital assay devices, especially pregnancy-testing devices and/or home-use assay devices, is that they provide an assay result as a signal of variable strength, which can require a degree of interpretation. This leaves the assay result open to misinterpretation, especially where the user or reader of the assay device has a preferred assay result in mind. In the case of some testing devices however, such as a pregnancy-testing device, it is preferred to configure the device such that no interpretation is required and the assay result is provided as one of two alternatives (i.e. pregnant or not pregnant). This may be described as a “binary outcome” device. This provides an unequivocal result which removes the need for interpretation by the user, which is undesirable. Current assay devices or assay device readers incorporate complicated optical and electronic components to read a variable strength signal and then provide a binary outcome via an electronic (e.g. LCD or LED) display.